Study of the phase dependency of RF cavities on gamma ray distribution

A front-to-end simulation study of a gamma irradiator was conducted, covering the entire process from the electron gun to the gamma rays going into a collimator, to investigate the impact of the RF phase on the irradiation process for continuous wave (CW) beams. Instead of considering an ideal monoenergetic beam to generate the gamma rays, we use a more complex simulation where initially, the electron gun generates a continuous beam of 50 keV ± 2.5 keV energy, which then passes through a multi-cell S-band RF cavity, accelerating the electrons to a final average energy of 6 MeV. Subsequently, the beam interacts with a tungsten plate downstream, generating gamma rays. An integrated simulation system consisting of specialized software for different study aspects has been developed. Poisson Superfish and CST Studio were used for RF cavity design, Travel for beam dynamics analysis, and Geant4 for simulating electron-gamma conversion and tracking. All beam properties were exported between codes in such a way that the particles position, energy, and RF phase dependency were preserved throughout. This work aims to define the realistic limits of the electron beam quality in RF electron linear accelerators for gamma irradiation.